1. Field of the Invention
This invention relates generally to the drilling of deep wells such as for the production of petroleum products, and more specifically concerns the acquisition of subsurface formation pressure data while well drilling operations are in progress.
2. Description of the Related Art
Present day oil well drilling relies heavily on continuous monitoring of various well parameters. One of the most critical inputs needed to ensure safe drilling is formation pressure. Presently, no formation pressure measurement is performed while drilling; only annulus pressure is measured. Various types of wireline tools, known as "formation testers," are currently in use which connect pressure sensors to subsurface formations intersected by a wellbore. The operation of such formation testers requires a "trip," in other words, removing the drill string from the wellbore, running the formation tester into the wellbore to acquire the formation data and, after retrieving the formation tester, possibly running the drill string back into the wellbore for further drilling. Because "tripping the well" in this manner uses significant amounts of rig time, which is very expensive, wireline formation testers are typically operated only under circumstances where the formation data is absolutely necessary or when tripping of the drill string is already being done for a drill bit change or for other reasons, such as having reached the desired depth.
During well drilling activities, the availability of reservoir formation pressure data on a "real time" basis is also a valuable asset for safely drilling a well. Drilling mud weight, used to control the wellbore pressure, is typically adjusted upon bit depth and drilling rates only. Real time formation pressure obtained while drilling will allow a drilling engineer or driller to make decisions concerning changes in drilling mud weight and composition as well as penetration parameters at a much earlier time to promote safer conditions while drilling.
The availability of real time reservoir formation data is also desirable to enable precise control of the weight on the drill bit in relation to formation pressure changes and changes in permeability so that the drilling operation can be carried out at its maximum efficiency.
It is desirable therefore to provide a method and apparatus for well drilling that enable the acquisition of formation data such as pressure data from a subsurface zone of interest while the drill string with its drill collars, drill bit and other drilling components is present within the wellbore, thus eliminating or minimizing the need for tripping the well drilling equipment for the sole purpose of running formation testers into the wellbore for measurement of a formation parameter.
It is therefore an object of the present invention to provide a novel method and apparatus for acquiring subsurface formation data while drilling of a wellbore is in progress, without necessitating tripping of the drill string from the wellbore.
It is a further object of the invention to acquire subsurface formation data in a time efficient manner so as to reduce the likelihood of the drill string becoming stuck in the wellbore and to reduce or eliminate disruption of drill string operations.
It is a further object of the present invention to provide such a novel method and apparatus by means of a probe that is moveable from a wellbore tool, such as a drill collar or a wireline sonde, to an extended position in engagement with the formation.
It is a still further object of the invention to provide such a probe that is adapted for substantially forming a seal at the wall of the wellbore as the probe is moved into engagement with the formation.
Known wireline conveyed formation testers have a toroid shaped rubber packer through which a probe nozzle is pressed against the borehole wall. After a local seal around the packer area is achieved, hydraulic communication through the probe is established and formation pressure is measured. Unless they are well protected, such rubber packers disintegrate rapidly under standard drilling conditions.
Also, the integrity of a packer seal relies on the existence of drilling mud and "mudcake" lining the wellbore wall. During drilling processes, the mud is circulated through the annulus between the wellbore wall and the drill string, reducing the amount of mudcake available for forming an effective seal at the wellbore wall.
It is therefore a further object of the invention to provide a method and apparatus for measuring formation parameters such as pressure that dispenses with the need for elastomeric packers or the like for achieving a hydraulic seal about a pressure communicating probe, and that forms such a seal at the wellbore wall during drilling operations when the extent of mudcake lining the wellbore wall is reduced.